The production of petroleum hydrocarbons from underground formations usually produces varying amounts of formation or connate water. The production ratio of "produced water" as it is often called, to petroleum hydrocarbons usually increases over the lifetime of a well. It is not uncommon that oil well production fluids are composed of 90% or more of water and only 10% or less of crude oil. Produced oilfield water contains a diverse mixture of compounds that varies from formation to formation. The term "water soluble organics" (WSO) has been used to describe a group of these components that are slightly water soluble depending on system conditions. These WSO compounds naturally occur in crude oil. WSO usually consist of naphthenates, carboxylic acids, lower fatty acids, and phenols. Water soluble inorganic salts present may include sodium chloride, sodium sulfate, calcium chloride, barium chloride, etc. While the amount of water soluble organics may be relatively small, up to 1,000 ppm, they nevertheless give rise to environmental problems when the aqueous phase is discharged into the environment without their removal. These compounds are included in the EPA recognized gravimetric analysis method used to monitor produced water discharges and sometimes make it difficult for producers to meet discharge requirements. In order to meet present day strict environmental standards, a process to reduce the level of the water soluble organics in the discharged streams to 50 ppm or less is needed. Furthermore, the water soluble organics may be valuable substances.
One of the first steps after removal of the oil well production fluid is to separate the oil from the water by phase separation techniques. Separation is conventionally accomplished using a bulk separator or a free water knock out system. Virtually all of the hydrocarbon is conveniently recovered in this manner. However, such traditional oil-water separation methods do not remove these WSO compounds from produced water.
Over the past several years, many methods have been utilized to remove WSO from produced water. Filtration with various types of media, membranes, ion exchange, bacterial degradation, oxidation, and acidification have all been tried with various degrees of success. For example, one could separate the water and water soluble organics by distillation or the use of biological treating ponds. Other methods include reverse osmosis, activated charcoal, and ceramic filters.
One common cost-effective method of treatment utilizes acids to lower the pH of the produced water and force the WSO components into the crude oil. Acidification and extraction of the WSO into the crude is simple, cost-effective, and requires very little additional equipment. The mechanism is simple: 1) the water soluble organic acid salts are converted to the oil soluble organic acids by lowering the pH, and 2) these oil soluble organics are extracted into the crude. However, there are significant disadvantages to this method, including, but not limited to, the hazards of handling acid, corrosion problems in storage and processing equipment, and reduced effectiveness of conventional water clarifiers.
For example, U.S. Pat. No. 5,364,532 involves oil well production fluids composed of oil and water and containing in excess of 100 ppm water soluble petroleum carboxylates in anionic form dissolved in the water which are treated by acidifying the fluid to a pH of 6.0 or lower with a combination of a strong organic acid and a strong mineral acid, which are then intimately mixed. The oil and water are separated one from the other. The content of the water soluble organics in the water is thereby substantially transferred to the oil phase.
U.S. Pat. No. 5,637,223 concerns treatment of oil well production fluids composed of oil and water and containing in excess of 100 ppm water soluble petroleum carboxylate in anionic form dissolved in the water by acidifying the fluid to a pH of 6.0 or lower with a combination of a strong organic acid and a strong mineral acid, and then intimately mixing them. The oil and water are separated from each other. The content of the water soluble organics in the water is thereby substantially transferred to the oil phase.
It would be desirable if a simple, economical procedure for accomplishing this end could be provided. While known non-acidic methods can reduce the content of water soluble organics to the desired low level, they are relatively complex and/or expensive.
Conventional water clarifiers predominantly remove insoluble oil and generally remove only small or very little amounts of WSO. Cationic products remove 10-20% of the WSO in produced water where cationic products are the product of choice.
It would thus be desirable to develop a composition and method employing it which did not require acid pH.